Wow. Great observation about the passive stuff on the debug session. There is your timeout and the cause for the delay..

The N::F documentation also mentions setting PASSIVE mode in the environment.. so early in the script .... $ENV{'FTP_PASSIVE'} = 1;
Will that do anything?

About those earlier values for sysctl - actually what I suggested (it must not have been all that clear, so sorry) was to see what the OSX system was set at with respect to TCP window sizes, etc. And then tweak from there.

The numbers in my OP were just placeholder numbers.. or values on systems here. So the goal was to try to go from a known bad state to a hopefully improved one. Also valuable would be to check the settings on the systems that were FTPing the files quickly, compare and match those settings on the faulty system, and see if it made a difference.

Another long shot - on that OSX system there isn't an exported environment variable ftp_proxy floating around is there?

... "put()" command), timing out after two minutes, then issuing the PASV command and doing it instantly ... what's that all about?

Have you found a bug in Net::FTP?